The iris recognition methods in the most widespread use comprise steps of acquiring an image of at least one eye of the user in an infrared spectrum, and of processing the image in order to extract identification characteristics of the iris as defined in the eye by an outer boundary. The identification characteristics relate to patterns that are present in the iris and that are specific to each individual.
Image acquisition was initially performed in the visible spectrum, but it was found that automatic pattern recognition was not very reliable for irises of dark color in which the patterns present little contrast. Image acquisition in the visible spectrum was quickly replaced by image acquisition in the infrared spectrum where the patterns present a high degree of contrast when compared with the remainder of the iris, thereby facilitating automatic recognition, regardless of the color of the iris.
Automatic recognition of iris patterns requires a prior step of locating the inner and outer boundaries of the iris in the image of the eye. Unfortunately, it has been found that although this operation presents no difficulties for the inner boundary, the outer boundary is sometimes located in inexact manner. It is found that in the infrared spectrum, the iris presents low contrast relative to the sclera which forms the white of the eye on the anterior portion thereof.